Selenium rectifiers and the method of making the same



Jan. 7, 1958 v c. s. SMITH 2,819,433

SELENIUM RECTIFIERS AND THE METHOD OF MAKING THE SAME Filed March 22,1951 2 Sheets-Sheet 1 Conduoiive'Bose 50nd Biqs'i' Nickei mare 'Firs'i'Series 0? Hoioger Corii'ciiniriq Selenium Layers in \li'l'reous FormConver'l'ing each Lager +o Clrg-si'ollime Form Second Series oFHoloqenConi'cininq qers in \/i+reous Form Selenium Lo Conver'i'inq. cili ILCHGFS +0 Cri s-i'ol'line F'orm i Pro duoinq Biocking Lager on Secondseries Clouni'er Elec'i'rocles Sprayed IN VEN TOR.

61E VE MA/D SCI/DEER (SM/77f WKMzz i His .4 +1 00) 85.

THE SAME C. 5. SMITH Jan. 7, 1958 SELENIUM RECTIFDIERS AND THE METHOD OFMAKING Filed March 22, 1951 2 SheetsSheet 2 PLAT|NG CONDUCTOR BASE Hi5A-H-arnay.

SELENIUM- RECTIFIERS AND THE METHOD OF MAKING THE SAME Smith,Indiana,gPa., assignor to Syn- Clevelanis dd r Homer City, Pa., a.corporation of Co p y. Delaware Application March 22, 1951, Serial-No.217,031- 18 Claims. (Cl. 317-234) This invention relates generally to,improved blocking layer devices and methods for producing blocking .a

layer dey ices,,and, more particularly to the method of producing dryplate rectifiers of the selenium type.

Thepr incipal object of-this invention is-the provision of ,a method fordepositing andfor controlling the .uniformity of aseries of seleniumlayers to. producea seleniumgcell, the uniformitybeing both, inlayerthickness and inlayer composition. This uniformity, is directional andvmay be controlled or maintained longitudinally and laterally of thecell.

Another object is theprovision of trollingv the thickness of the.selenium layers in a blocking device to make them suitable for apredetermined voltage ratin'g A thicker selenium layer is required, forhigher voltages and .the method comprising this invention permitsevaporation .of selenium to produce layers of any desired thickness to..build a suitable deposit ,for'predetermined voltages.

This process insures a comparatively "flawless selenium deposit'of' theproper type of crystalline; structure for high quality rectification.selenium layers is deposited as black amorphous seleniurn whichjiscaused to crystallize to the correct, crystalline form before the. nextlayer is deposited thereon. Any particles on anylayen are quicklycovered, which produces averygood and .uniform composition,

"Another object of thisi. invention. is the .method of controlling, thehalogen concentration in each selenium deposit on the conducting base. Arelatively high per- 'centage of'halogen. concentration isin the firstlayers deposited on thebase. The final layerseither have relativelyl'oyvor no halogen concentration. ,When-there is nohalogen in the finallayers of selenium thedeposits are heated lo control the migration ofhalogens from the-first layers to the final layers. It is :important toaccuratelycontrol the halogen layers to lower the resistivity but not.enough to inhib it the ability to develop and form a blocking layer,This control provides a favorable resistivity gradient in the layers.

Anothenobject-isthe methodof producing large-area blbckinglayer devicesat low cost .mass production.

Another'object is the method of reducing the cost of production-ofblocking layer. devices by applying the vapori zedj deposits through avery shortand uniform. dis ta'nce'which reguires less expensive vacuumpump equip ment--tooperate;

Another obiect is the provision of the method, of manufacturingblockinglayer devices. This method not only includes-thesequence ofsteps of producing the blocking-layer devices but also the timing of thesteps together-with therate--andthickness of thedeposits. Thisnmethodaembraces a continuousprocessfor the production of the blocking layerdevices;

Another object. is the. provision-ofthe a method. for con-Each.layer.,.of the. series of concentration in the final 7O method of acoating opposite surfacesi of oneiconductor base plate r or Ivery shortintervals, between,

ice

the outer surfaces of two conductor base plates simultaneously whenassembled back to back.

Other objects and advantages appear ing description and claims.

The invention may best be understood by reference to the followingdescription taken in conjunction with the drawing in which:

Fig. l is a fiowsheet diagram showing the procedural stepsemployed inthis invention.

Fig.2 is -a sectional view of a blocking layer rectifier produced inaccordance with this invention.

Fig. 3 is a graph illustrating the rate of selenium deposited.

Inthe processcomprising this invention a series of selenium layers may,be added consecutively as separate deposits or they may. be deposited intwo independent .and separate steps. A master selenium .mix is employedfor each deposit; .These master selenium mixes may each-,containa-highproportion of one of the halo-gens; iodine, bromine, chlorine orfluorine, or the second deposit may be free, of a halogen. A- halogencontaining master .rnix is added toselenium, in predeterminedproportions for producing, deposited layers in the first phase or, the,first step and the other halogen containing master mix ris addedinpr'edetermined proportions to another batch of selenium or thehalogen-free selenium batch is'used for, producing the second series oflayers. There is. a greater halogen concentration in the bntchforthcfirst deposit of thelayers. than in the batch for the so"- ond depositof the layers. 1

The. layers, of each depositare evaporated, on a conducting base in arelatively short period of time and with the .deposit of each layer andthe time periodbetween. the firstandsecond. deposits ofthe two seriesoflayers. maybe greater ,thanthe. time interval between the deposit ofconsecutive layers,.which is a matter of a fraction of a minute, Theconducting base or sheet maybe mounted in'arc shapetor rotation aboutacentral ,axis' in .a vacuum with .the surface of the conducting base,less than .one inch from .the evaporator which is mounted in afixedposition to deposit, agreat many thin finite layers of selenium. invitreous ,form in a first series as the. arc-shaped sheet rotates, Each.of the deposited finite layers of selenium. islheated to convert. it

in the follow- "to crystalline formv before: the next finite. seleniumlayer is-deposited. The temperature is regulated and .the deposits aremade'in' a vacuum .with relative movement between the conducting baseandthe. vaporizer. Thisrelative movementpermits a seriesof finite layersto.bedeposited at intermittent intervals enabling one. to control theultimate thickness of the deposited layers and their uniformity. Theseare very important advantages of. this process. A great many finitelayers, -of selenium in vitreous form may be depositedlasthe firstseries-of layers. on theconducting base. as. the latter. continuestorotateto build up a second seriesrof-finitelayers whicha'reconvertedto. crystalline form..

The. blocking. layer device, of -this-vinvention comprises the. metalconductive baseal' which-functions :as." the car'- rierelectrode andiispreferably: an aluminum alloy know n as' Duralumin. A largeasheetof'thi's aluminumis first sandblasted.toxprovidei a uniformroughenedsurfaceu A grit size ofapproximatelytZZO' mesh siliconcarbide-is employed touproduce peaks and valleys, the dimensions, ofwhich-are-small compared to the three to four thousandtlis inch seleniumthickness.- This sandblast time is deter? mined experimentally andreduces the forward rectifier resistance to a minimum.

The=blasted-aluminum sheet'is then placed in a suitable' bath and lightnickel plated indicated by thelayer 2. This light nickel coatingimproves the electrical contact between the selenium and the aluminum.

The sheet, when in a vacuum, is then passed over a temperaturecontrolled vaporizing pot which contains the selenium to be deposited onthe sheet. The conducting base is mounted arc shape tor until it is allgone.

The first series of layers is made from a batch of selenium havingapproximately one halogen atom to approximately 2,000 selenium atoms. byweight of the first batch and it contains approxisistivity of thissecond series of layers.

A halogen-free selenium halogen atoms that would blocking layer. Thus ineither mode the second series of layers contain halogen atoms.

The conducting base sheet is repeatedly passed over the seleniumevaporators and each time an additional of selenium is evaporated ontothe sheet.

produced. The thickness of the selenium determines the ability of thecell to prevent arcing be tween the counter electrode and the base.Roughly .15 mill of selenium is needed per bolt of R. M. S. inverse S.cell requires a selenium deposit 2.7 mills thick, a 26 volt cellrequires 3.9 mills of selenium and a 40 volt cell requires 6 mills ofselenium.

The selenium batches containing the master mixes are of the cells beingpoured into the evaporators in molten form and are quickly cooled tomaintain the black vitreous form. Heat is then initially applied to theplate in vacuum, and relative movement is made between the plate and theevaporator with a very short distance, less than one inch, between them.Sufiicient heat is applied to the evaporator to approximately C. therate of the deposit is very rapid, as indicated by section B of thecurve, until the ultimate rate of evaporation takes place throughout theperiod C. When the plate is above 120 C. the black vitreous deposit isconverted to crystalline form before the next the second evaporator todeposit the second series of layers on the first series. Being amaterially less quantity it takes the second batch only a short time tobe com- After the selenium deposits have been made the plate C. for asufiicient length of time to heat-treat the cell and improve itselectrical characteristics. If the second series of deposited layers ofselenium are halogen-free then sufiicient time must be given to permit"biomass of layers with the halogen containingthe selenium component isthen-evaporated *on the plate as the subsequent heat treatment willnot-"diffuse the halogen atoms fromthefi'rst to the secondlayersto-avery great extent. This subsequent insure that all of theblack vitreous' deposits have. been converted to .the crystalline state.

It has been found experimentally, that better quality is obtainable whensecond selenium component deposits are in .the black vitreous to heattreating temperature to convert this amorphous form to the crystallinestate. The reason for this improvement -is--believed to be due-"to theslow-rate of diffusion of the halogens through selenium to the secondlayers. *It requ'res approximately 30 seconds to begin crystallizing andapproximately another 30 seconds to approach full crystallization whichis a minutes time in which very little halogen could diffuse into thesecond layer. Full crystallization may be reached in 2 to 5 minutes atwhich time the halogens difiuse faster, but due to the slow start itdoes not have time to reach the second series in any appreciablequantities by the time crystallization is complete.

After heat treatment the plate may be exposed to an oxidizing agent todevelop a selenium oxide film on the second series of layers to form abarrier layer.

After the formation of the barrier layer by producing an oxide thereon,the plates are suitably masked as to ultimate shape and size and thecounter electrodes are sprayed on the oxide film and electroformed inmethods familiar to the art. Finally the plates are punched and shearedto the particular sizes required.

The conducting base material is preferably a large sheet, plate or longstrip and may have selenium layers vaporized on both sides thereof atthe same time in which instance a portion of the base material is baredto obtain or to attach a conductor. Again the conducting base materialmay be two sheets, plates or long strips placed back to back for thepurpose of having the selenium layers vaporized at the same time on eachconducting base material. The use of the term conducting base materialin the claims is defined to include both sides or one side of eachsheet, plate or strip placed back to back for vaporizing seleniumthereon at the same time. In either event the selenium layers are of thesame consistency and are applied under the same conditions and in thesame steps as previously described.

An extremely high quality plate may be produced by suitable adjustmentsof the first and second series of layers of theselenium component as tothickness and composition. By treating large size plates and afterwardspunching and shearing them to size, very high production may be obtainedat relatively low cost.

I claim:

1. The method of producing a selenium rectifier on a conducting sheetwhich comprises the steps of repeatedly passing the conducting sheetover the discharge of a temperature controlled vaporizer in a vacuum todeposit thereon a great number of very thin layers of vitreous seleniumto produce on the conducting sheet a coating made up of a series offinite layers, heating the vitreous selenium to convert it intocrystalline form, thereafter producing a blocking layer on the surfaceof the crystalline selenium, and applying a counter electrode on theblocking layer.

2. The method of claim 1 wherein the conducting sheet is firstsandblasted and then immersed in a bath to apply a nickel coat thereto.

3. The method of claim 1 wherein the speed of movement of the conductingsheet over the evaporator controls the thickness of each finite layer ofselenium and the total number of times it is passed over the evaporatorcontrols the number of layers.

4. The method of claim 3 wherein the conductin heat treatment need'o'nly besu'flicient to form andthen rapidly brought the black vitreousaxis to repeatedly passit's surface over the vaporizer.

5. 'The methodof laimf4 wherein hesur'face'iof the sheet is less than aninch from the" discharge The method "of claim 1 'wher'ein'the conducting"sheet is progressively moved over the discharge "of the vaporizer whileeach finite layer 'o'fselenium' is applied thereto. A

7. The method or claim 1 wherein'e'ach'finite layer is applied invitreousform and then converted by heating to crystalline form whilemovementof the conducting thenext finite layer is applied '8. The methodofcla'im 1 which alsofincludes the steps "of dep'ositingthefiniteselenium layers in two series 9. The method of claim 8 which alsoincludes the step of heating the first series of deposited layers as acoating before applying the second series thereto.

10. The method of claim 1 which also includes the steps of depositingthe finite selenium layers in two series of layers, the first seriescontaining approximately one halogen for every two thousand seleniumatoms and the second containing no halogen.

11. The method of claim 10 which also includes the step of applying heatto the second series of finite layers of selenium for a sufiicientperiod of time to diffuse some of the halogen from the first series oflayers to the second series of layers.

12. The method of claim 10 which also includes the steps of convertingeach finite layer of the first series by heating to crystalline formwhile movement of the conducting base subsists and before the next layeris applied thereto, heating the first series of deposited layers toinsure complete crystallization before the second series of layers areapplied, and heating the second series of layers for a sufficient lengthof time to convert the selenium from vitreous to crystalline form butprevent the halogens from reaching the surface of the second series oflayers.

13. The method of claim 1 which also includes the steps of depositingthe finite selenium layers in two series of layers, the first seriescontaining approximately one halogen for every two thousand seleniumatoms and the second containing a still smaller percentage of halogen.

14. The method of claim 1 wherein the conducting sheet is large and thecounter electrode is applied in its ultimate size and shape and theconducting sheet is thereafter punched and sheared to the size of use ofthe rectifier cut therefrom.

15. The method of claim 1 characterized in that the shape of saidcounterelectrode is one of a multiple of ultimate sizes and shapes.

16. The method of producing a selenium rectifier on a conducting sheetwhich comprises the steps of repeatedly passing each side of theconducting sheet simultaneously over the discharge of temperaturecontrolled Vaporizers in a vacuum medium to deposit on each side a greatnumber of very thin layers of vitreous selenium to produce on each sideof the conducting sheet a coating made up of a series of finite layers,heating the vitreous selenium to convert it into crystalline form,thereafter producing a blocking layer on the surface of each series ofcrystalline selenium, and applying a counter electrode on each blockinglayer.

References Cited in the file of this patent of each conducting sheetsimultaneously over the (118- 1,784,611 charge of temperature controlledVaporizers in a vacuum 2,189,576 medium to deposit on the outer side ofeach sheet a great 2,367,943 number of very thin layers of vitreousselenium to produce 2,45 3,763 on each sheet a coating made up of aseries of finite layers 21476'042 heating the vitreous selenium toconvert 1t mto crystalline 2,481,739 form, thereafter producing ablocking layer on the surface 10 215 01331 of each series of crystallineselenium, and applying a 2,524,270 counter electro e on each blockinglayer.

8 A selenium rectifier comprising a conducting sheet 482 239 havingapproximately fifty or more of very thin super- 629869 imposed finitelayers of selenium in crystalline form a 15 632:752

current blocking layer on the topmost selenium layer,

layer.

UNITED STATES PATENTS Polyani et a1. Dec. 9, Brunke Feb. 6, Hein Jan.23, Smith Nov. 16, Hewlett July 12, Goodman Sept. 13, Hein Mar. 21,Pelfrey Oct. 3,

FOREIGN PATENTS Great Britain Mar. 25, Great Britain Sept. 29, GreatBritain Dec. 5,

1. THE METHOD OF PRODUCING A SELENIUM RECTIFIER ON A CONDUCTING SHEETWHICH COMPRISES THE STEPS OF REPEATEDLY PASSING THE CONDUCTING SHEETOVER THE DISCHARGE OF A TEMPERATURE CONTROLLED VAPORIZER IN A VACUUM TODEPOSIT THEREON A GREAT NUMBER OF VERY THIN LAYERS OF VITREOUS SELENIUMTO PRODUCE ON THE CONDUCTING SHEET A COATING MADE UP TO A SERIES OFFINITE LAYERS, HEATING THE VITREOUS SELENIUM TO PRODUCE ON THECONDUCTING SHEET A COATING PRODUCING A BLOCKING LAYER ON THE SURFACE OFTHE CRYSTALLINE SELENIUM, AND APPLYING A COUNTER ELECTRODE ON THEBLOCKING LAYER.
 18. A SELENIUM RECTIFIER COMPRISING A CONDUCTING SHEETHAVING APPROXIMATELY FIFTY OR MORE OF VERY THIN SUPERIMPOSED FINITELAYERS OF SELENIUM IN CRYSTALLINE FORM, A CURRENT BLOCKING LAYER ON THETOPMOST SELENIUM LAYER, AND A COUNTER ELECTRODE ON SAID CURRENT BLOCKINGLAYER.